Fibroblast-Cardiomyocyte Cross-Talk in Heart Muscle Formation and Function

Abstract

Cardiac fibroblasts make up a considerable fraction of the total heart cell content. How cardiac fibroblasts signaling affects heart muscle function in normal heart development and disease remains, however, largely unresolved. Engineered heart muscle (EHM) developed from human pluripotent stem cell-derived cardiomyocytes (CMs) and fibroblasts in a collagen I hydrogel can be considered a human heart surrogate, allowing for precise assessments of fibroblast-CM crosstalk under defined in vitro conditions. We hypothesized that EHM development and function are controlled by fibroblast-mediated cardio-instructive cues. In line with this hypothesis, we found that macroscopically contracting EHM fail to form in the absence of fibroblasts. Biophysical analyses confirmed that fibroblasts control early collagen gel compaction and stiffening, suggesting a fine-tuning function as to the biomechanical properties of the extracellular matrix (ECM) environment. Transcriptome data suggested that EHM formation in the presence of fibroblasts recapitulates important aspects of early cardiac morphogenesis, including cardiac cushion formation. In line with these findings, we identified hyaluronan (HA) as a crucial component of EHM development and function. However, excessive HA deposition resulted in functional deterioration of EHM, pointing to the need for a fine-tuning of fibroblast-mediated processes during cardiomyogenesis. By systematically comparing primary fibroblasts of different origin (skin, gingiva, cardiac) to their cardiomyogenesis-supporting activity, we found that the developmental cues needed for EHM formation were to a certain extent universally present in all tested fibroblast species. We further observed that fibroblasts from patients with dilated cardiomyopathy (DCM) elicited a pathological contractile phenotype, underscoring the relevance of fibroblast-CM crosstalk in health and disease. Collectively these findings provide strong evidence for the active role of fibroblasts in determining development, function, and disease states of the human heart. To further improve our in vitro model and allow for the future use of EHM in vivo, we developed EHM under chemically defined conditions. We furthermore identified pluripotent stem cell (PSC)-derived cardiac fibroblast-like cells as a potential source of fibroblasts for EHM application.